The compressional behavior and the P-induced crystal-fluid interaction of a natural paulingite-K have been explored on the basis of in-situ single-crystal and powder X-ray diffraction, and in-situ single-crystal Raman spectroscopy with a diamond anvil cell and a series of diverse pressure-transmitting fluids (i.e., silicone-oil, methanol:ethanol = 4:1, methanol:ethanol:water = 16:3:1). No evidence of any phase transition was observed within the P-range investigated, independent on the used P-fluids. The compressional behavior of paulingite is significantly different in response to the different nature of the P-fluids. A drastically lower compressibility is observed when the zeolite is compressed in methanol:ethanol or, even more noticeably, in methanol:ethanol:water mix. We ascribe this phenomenon to the different crystal-fluid interaction at high pressure: (1) silicone-oil is a "non-penetrating" P-medium, because of its polymeric nature, whereas (2) methanol-ethanol and water are "penetrating" P-fluids. The P-induced penetration processes appear to be completely reversible on the basis of the X-ray diffraction data alone. The Raman spectra collected after the high-pressure experiments show, unambiguously, that a residual fraction of methanol (and/or ethanol and probably even extra H2O) still resides in the zeolitic sub-nanocavities; such molecules are spontaneously released after a few days at atmospheric pressure. The actual compressibility of paulingite-K is that obtained by the compression experiment in silicone-oil, with an isothermal bulk modulus K0 = β0-1 = 18.0(1.1) GPa. Paulingite appears to be one of the softest zeolite ever found.
Bibliographical noteFunding Information:
GDG acknowledges the Italian Ministry of Education , MIUR-Project: “Futuro in Ricerca 2012 – ImPACT – RBFR12CLQD”. KSS and RM gratefully acknowledge the financial support from the University of Vienna (Grant BE532003 ). RS acknowledges the support through the institutional project RVO 67985831 of the Institute of Geology AS CR , v. v. i. YL thanks the Global Research Laboratory Program of the Ministry of Science, ICT and Planning (MSIP) of the Korean Government. Experiments at PAL were supported in part by the MSIP and POSTECH . Two anonymous reviewers and the Editor (P. Wu) are thanked.
All Science Journal Classification (ASJC) codes
- Materials Science(all)
- Condensed Matter Physics
- Mechanics of Materials